I was not aware that other people didn’t know about this until recently, but since it seems to be little known, I thought I’d write a post on the topic.

In WordPress, you should never start the custom permalink string with any of these %postname%, %category%, %tag%, or %author%. (Unless you know what you’re doing, of course. )

Meaning that “%category%/%postname% ” is a bad custom permalink string. So is just “%postname%” for that matter.

Why? Well, it has to do with how the WordPress Rewrite system works.

Rewriting Explained

See, when you request a URL from a WordPress site, WordPress gets the URL and then has to parse it to determine what it is that you’re actually asking for.

It does this by using a series of rules that are built whenever you add new content to WordPress. Generally the list of rules is pretty small, but there are specific cases that can cause it to balloon way out of control.

Normal Rules

Let’s say you’re using a normal permalink string, like my preferred “%year%/%postname%”. The rules that are generated will look like this:

The way that system works is that it compares the URL it has to each of those in turn, from the top to the bottom. When one of them fits, then WordPress knows what to display and how to do it.

Note that the order I listed those in is is significant. Each one from the top down is less specific than the previous one. For example, “robots.txt” matches only that, while “/feed/*” matches anything starting with /feed/. And so on down the list. The %postname%, %category%, %tag%, %author%, and %pagename% will match any string, but the other WordPress % ones will only match numeric fields. Like %year% is always a number.

Notice that the last one is %pagename%. This basically matches everything, because %pagename% can be anything at all. Even hierarchical pages like /plugins/whatever/something will cause this to match. It’s the fall-through position. And then, if that page doesn’t actually exist on your site, then this causes the query to trigger the 404 condition internally, which causes your theme’s 404.php to load up.

Pretty simple and straightforward, really.

Problem Rules

The problem comes in when you try to use a non-number for the beginning of your permalink string. Let’s examine those last two rules closer:

That violates our main rule, doesn’t it? That each one should be less specific than the one above it? Because %category% can match any string too, just like the %pagename% can… With this set of rules, there’s no way to view any of the Pages. Not good.

So, WordPress detects this condition and works around it. Internally, this sets a flag called “use_verbose_page_rules”, and that triggers the rewrite rebuild to make this set of rules instead:

/robots.txt (for the privacy settings)
/AAA
/BBB
/CCC (one of these for each of your Pages)
/feed/* (for normal feeds of any kind)
/comments/* (for comments feeds)
/search/* (pretty url for searches, not often used)
/category/%category% (category archives)
/tag/%tag% (tag archives)
/author/%author% (author archives)
/%year%/%month%/%day% (with each of those after year being optional)
/%category%/%postname% (this is the permalink string you define)

Now we have basically the same set of rules, except for those new ones at the top. Every Page now gets its own very specific rule, and this satisfies our main condition once again.

Pages

But what if you have a lot of Pages? I once read a post by a person who had over 50,000 Pages on his site. That is a special case obviously, but consider our lookup system. We’re going through these rules one at a time. With our first method, our rule list was only 10 rules, maximum. With this new method, you add a rule for every single Page you make. Going through 50,000 rules takes a lot longer than going through 10. And even just building that list of rules can take a long time.

Basically you’ve created a performance issue. Your Pages now won’t scale to unlimited numbers. Your site’s speed is linearly dependent on the number of Pages you have.

This is a bad thing.

Conclusion

Firstly, it’s really not any better for SEO to have the category in there, or to have just the postname there by itself. And anybody who tells you differently is wrong. If you disagree with me, then no, I’m not interested in arguing this point with you; you’re just wrong, period, end of discussion.

Secondly, shorter links are great and all, but hell, why not use a real shortlink? WordPress 3.0 now has a ShortLink API that defaults to using ?p=number links on your own domain. These will actually work for any WordPress site, even ye back unto WordPress 2.5. WordPress 3.0 just makes it nicer and easier to use these with the Shortlink API (as well as allowing plugins to make this automagically use services like wp.me or bit.ly). So use that instead.

The conclusion is, in general, just don’t do it. Leave a number, or something static, at the beginning of your permalink string and you’ll never have any sort of problems. But if you really MUST do this sort of thing, then keep your number of Pages low. Don’t try it when you have more than, say, 30-50 Pages.

Addendum

Okay, so I actually simplified things for this post. It’s actually worse than this, as verbose page rules can add much more than one rule per page, as this post demonstrates (he gets 11 per extra page!).

Never thought I’d say this… But my recommendation for people thinking about upgrading from a single-user WordPress 2.9 installation to WordPress 3.0: Don’t do it… yet.

WordPress 3.0 is such a major update, that for 95% of the single-user blogs out there, I would recommend putting it off and not upgrading at all. Not until the issues are worked out.

See, everybody is talking about the features of 3.0, and those are indeed many and varied. But not many people are talking about the problems of 3.0. And while it is only in beta, it’s not too early to consider some of the design choices here and think about them in a larger scope.

Theming

Firstly, understand that a lot of the new features require theme support. Meaning that your existing theme, while it will work, won’t give you the new menuing system, it won’t have the comment form enhancement, the new editor styling tricks won’t work, etc…

So if you’re going to upgrade to 3.0 without modifying your theme as well, you’re not going to get the full experience.

The new Twenty Ten theme, while it is neat and shows off what can be done, is very, very complicated (and IMO, it also does a lot of things very badly). It’s somewhat difficult for even an experienced theme editor and developer to understand, so expecting a normal blogger to read this as an example and then change their own theme as needed is somewhat nutty. So if you want these new features, you’ll probably need professional assistance to get it all up and working.

Custom Post Types

They’re neat, they’re cool, and they’re insanely difficult to use properly. What’s going to happen here is that people will use them badly at first. Incredibly badly. Some of the examples I’ve seen thrown around are surprising just for the sheer crazy. Yes, you can make a “Podcast” post type, but do you really want to? Does it really make sense in the context of what you’re doing? The answer is probably not, actually.

And using them changes so much internally to the system that things start behaving in ways you totally don’t expect (or see). For example, custom post types don’t show up in feeds by default. That might make your podcasting a little bit, shall we say, broken?

Now, custom post types have to be enabled by plugins and such, so those plugins might indeed take care of this sort of thing properly. But frankly, I wouldn’t want to bet on it. People are going to have all sorts of weird problems with this until they work out that they really didn’t need custom post types after all.

IMO, only a very limited subset of people need this, or think they do, and those people are very likely already using them in some manner.

Plugin incompatibility

Any plugin that deals with posts being published is likely to be affected by custom post types. And this won’t be limited to your custom posts.

I’ve already had to edit 4 different plugins I use (2 of them are mine, admittedly) because of the new menu system. It stores the menu items in it as posts with custom post types of “nav-menu-item”. So before I fixed it, making a new menu item would cause the name of that menu item to appear on my Twitter feed. Simple Twitter Connect was seeing a new post get created, and it dutifully published that fact. It simply didn’t expect a “post” to be a “menu item”.

I’ve currently hardcoded the plugins to limit them to seeing actual posts and pages, but that seems a poor solution to me. What if somebody wants to make that “podcast” post type? How is a plugin supposed to know what is really a post and what is not? Overloading the wp_posts table for storage of “not-posts” in this way is confusing and strange and it’s going to break a lot of plugins.

So at the very least, don’t upgrade until your plugins explicitly support 3.0.

Menus

The new menu system is clever, but ultimately very limited. I tried it, but I eventually opted to not use it at all.

The problem is that it’s wholly static. Every menu item is a name and a URL, basically. There’s nothing there to make dynamic menus from your content. Like my WordPress Plugins dropdown at the top of the page there. That’s generated by a call to wp_list_pages. Can’t do that with the menu system. And generating a dropdown menu of a given internal list seems, to me, to be a strangely missing piece of the whole thing.

You can make that same menu manually, but if you add a new page, you have to go and manually add it to the menu as well. And that’s all well and good for people who want to micro-manage their site. I’m sure they’ll love it. But I can’t say that I do.

Now, I have been having this argument on the wp-hackers list, so it’s entirely possible that the final release will address more than a few of my above objections. So plugins might be created to fix this issue. Hell, I might create a few of them myself. But in the end, I still find that the underlying design is fundamentally flawed. The system stores menu items as metadata attached to fake posts. In my opinion, that’s just nine kinds of crazy. They should have leveraged the existing widgets system instead, and perhaps have made a new table to hold widget and menu item data together (thus solving the widget data problem and having a place to put menu-items all in one shot). Not everything should be a post.

Multi-Site

Okay, yeah, Multi-Site is damn cool, for those of us that run more than one site. But it’s got issues too. Mainly, it’s just complicated.

It’s complicated in that there’s several types of choices to be done. You have to know server configuration. You have to understand DNS and static IP addressing. Knowledge of Apache and VHOSTing helps. And if you’re using multiple domains, which seems like a rather common setup, then you’re into mu-plugin territory, which is wholly new to anybody familiar only with WordPress and not WordPress MU.

Setting up Multi-Site for my two domains required the following steps:
1. Move WordPress to the root of my domain (it really doesn’t work in a subdirectory. Just trust me on this).
2. Enable multisite by editing wp-config.
3. Enable it in the interface, making choices that I didn’t understand. The difference between a subdomain and a subdirectory installation is not immediately apparent, and later turns out to be wholly irrelevant when you use the Domain Mapping plugin anyway. Answer for everybody else: Subdirectory is simpler and requires less configuration, subdomain only works if you have more server control than the average cheap hosting account gives you (static IP, wildcard DNS, VHOST, etc).
4. Copy and paste a whole bunch of stuff that WP spits out into my wp-config and htaccess files.
5. Install the Domain Mapping plugin (manually install, you can’t do this through the happy plugin install interface, because it requires putting files into various directories).
6. Configure the mapping. This is confusing at first, because after you get it working and give it the server IP, you have to actually go to each site’s individual wp-admin in order to map it to a domain. Not hard, but very unclear. Oh, and before you map the domain, make sure that the domain is actually pointing to your server IP, because the mapping takes effect instantly, with no way to undo it. I had to manually edit my database to undo it after I screwed this up the first time.

After all that, there’s still a few bugs. Minor stuff though. The links on dashboard on the main site aren’t quite right. My main site shows individual posts in the /blog directory, with no real way to remove it (it’s hardcoded and deep in the heart of things there’s probably a good reason for it, but it’s still annoying). There’s some other limitations which are too boring to go into.

BTW, if you’re already running MU, then go nuts. This upgrade is perfect for you. It’ll get you onto the main line and that is more important than anything I’m talking about here.

Note that I’m not sure that this is fixable. Multi-Site is complicated by its very nature. Integration of Domain Mapping into the core would help make this a lot simpler and would have the side benefit of eliminating the unnecessary subdomain/subdirectory choice. But ultimately, you do have to have some server-side config to make this sort of thing work, and that’s never going to change.

Not everything is bad

Don’t get me wrong, there’s lots and lots of good stuff here. The Shortlinks API is great. The plugin and theme updaters have been enhanced and moved around proper. A lot of the new theme stuff like the header trickery and the automatic-feed-links and such are very cool.

I like the direction WordPress is heading. I just think that this particular stop on the tracks is not a great one. Too much still unfinished and only halfway thought-out, IMO.

And again, I realize that this is beta code, and I’m not criticizing any of the developers or talented individuals working on it. I get that WP 3.0 is unfinished as of this writing. I’m just trying to look at this from a perspective of an end-user. What’s in this upgrade for the end-user? Ultimately, not very much.

So while 3.0 is a very, very good step in the right direction, it’s a step that that end-users might want to skip over for now. If you’re a WordPress hacker, then go nuts. You’ll be fine with 3.0. But if not, then you might want to hold up a while and wait for the next release instead.

Note that this won’t stop me from upgrading, nor from posting tips/tricks for 3.0 users. Just saying.

I’m switching all my sites over to a single 3.0 installation, with the new MultiSite capabilities. So the sites might be fruity for a while. In the process, I also expect to lose some things, such as the email subscriptions. Sorry about that, I’ll restore stuff like that later.

Sorry about that, folks. An inadvertent early check-in made it so some bugs crept into the releases I had scheduled today. I didn’t mean for those to get released when they did, and I didn’t notice it for a couple hours. So some people may have upgraded earlier than I wanted them to.

Versions 0.16 of Simple Facebook Connect and 0.6 of Simple Twitter Connect should not be used. Wait for the 0.16.1 and 0.6.1 releases to hit the repository. Those will work without the same sorts of errors.

If you are already having the major fatal error with Simple Twitter Connect, then delete the stc-comments.php and stc-publish.php files to make your site work again. Then upgrade to 0.6.1 and the working files will be restored.

Over on my Simple Facebook Connect page, there’s lots of comments from users with problems. Having answered these for a while now, via there and via email, I’ve come to the conclusion that people don’t search for answers to their problems.

The “How to fix the Email Domain” problem is answered on that one page no less than 6 times, for example. Almost all the rest of the problems given come from the “wrong connect URL setup” issue.

So if you don’t want to do support all the time, I think you have to make your plugin smarter. Take the most common issues you see and make the plugin auto-detect the problems. That’s what I’ve done with SFC version 0.16, for example.

Error messages now show up when the user configured something wrong on Facebook.

The plugin now can detect these two major causes of problems and will display an error message. It also provides a link to the right place on Facebook to go and correct these problems. It can’t actually fix the problems directly (though that is possible… small steps), but I hope this will eliminate the need for me to continually have to answer the same questions over and over again.

So my tip for the day for plugin programmers: For robustness, make your plugin check for commonplace issues. And the issues that you think will be commonplace may not be the ones you expect, so figure on having to add more and more checks every time.